1. Field of the Invention
The present invention relates to a process for producing titanium-containing cold rolled steel sheets and strips (hereinafter called steel strips) which can stand very severe press forming.
2. Description of Prior Arts
Up-to-now many inventions have been made regarding press forming cold rolled steel strips per se and processes for producing such strips.
For production of non-ageing steel strips with improved drawability by continuous annealing, it is known, as disclosed in Japanese Patent Publication No. Sho 50-31531, to add aluminum and then titanium to a molten basic steel composition containing 0.001-0.020% carbon and 0.30 to 0.60% manganese, so as to maintain the sol.Al content not less than 0.01% and the Ti/C ratio not less than 4 to obtain a steel slab having good surface quality, and to subject cold rolled steel strip obtained form the slab through hot rolling, acid-pickling and cold rolling to continuous annealing by heating the strip in the temperature range of from 750.degree. C. to Ac.sub.3 point with a heating rate not less than 500.degree. C./hr., holding the strip at this heating temperature for not longer than 300 seconds.
However, this prior art adopts a low temperature coiling in the hot rolling and has a disadvantage that a high degree of drawability, particularly the r value and the elongation, cannot be obtained without a relatively high level of titanium content.